The present invention relates to a system for automatically detecting and setting the focus of an optical system.
Heretofore many methods have been proposed wherein focus detection is performed by radiating a beam or ray from a ray or light emitting device fixed on an apparatus. The light is reflected by an object to be detected and then sensed by a light or ray receiver. However, when this kind of system is actually used, the amount of the incident light entering the ray receiver varies over an extensive range on the basis of the difference in the distance to an object or on the refractive mirror of the apparatus.
The operating range of an electronic circuit must be quite extensive. Unless this is so the function of entire system is apt to become unstable and great difficulties may be encountered.